Selective program distribution system



Feb. w, 1942. R. c. CURTIS 2,272,999

SELECTIVE PROGRAM DISTRIBUTION SYSTEM Filed April 10, 1941 2 Sheets-Sheet l T STANDARD TRANSMITTERl INVENTOR ATTORN EY R. c. CURTIS 2,272,999

Filed April 10, 1941 2 Sheets-Sheet 2 I 83 A c 2596 1055mm Q U 028mm Ewin m\ Q wmii Qz 5315s o W\ w w ESE mm a I Qz m x uxmm. Ii mokum mw w M SELECTIVE PROGRAM DISTRIBUTION SYSTEM Feb. 10, 1942.

INVENTOR Rill nrfi E. Euriiis ATTORNEY 000M h ml: filial .l. L G

Patented Feb. 10, 1942 SELECTIVE PROGRAM DISTRIBUTION SYSTEM Richard 0. Curtis, East Orange, N. J assignor to Wired Radio, Inc., New York, N. Y., a corporation of Delaware Application Apr-ii 10, 1941, Scria1No. 387, 934

6 Claims. .(Cl. 250 s This invention pertains to broadcasting systems and relates in particular to a novel type of broadcasting system of such nature that while the program to be distributed is radiated in the usual unrestricted manner and may be received by any ordinary receiver, it can only be satisfactorily received in comfort and with pleasure by an authorized listener by means of a special receiver. The system might well be termed an authorized or selective program distribution system.

Space radio broadcasting as at present constituted is provided as a free service to any listener having a receiver such as is obtainable on the open market. The expense involved in such broadcasting is in general defrayed by the sale of time to sponsors, usually national advertisers, who are permitted to utilize, to the annoyance of most listeners, a portion of their time on the radio for advertising purposes.

This invention proposes a method of space radio broadcasting which cannot be satisfactorily received in a manner comfortable and pleasurable to the listener on any receiver available on the open market. Receivers which will satisfactorily receive the proposed type of broadcast can be readily manufactured and leased by the broadcaster to the listener to thus permit furnishing a program of high quality and fidelity without the annoyance of interruptions for advertising purposes. As the listeners pay the broadcaster directly for the service, the broadcaster is able to furnish a high grade service which is self-sustaining.

In general, the proposed novel system contemplates the addition of disturbing energy in the audible range to the program energy normally used to modulate the transmitter, and in addition modulation of the transmitter with a second carrier preferably slighly above the audible range. This second carrier is also modulated by the disturbing energy above referred to. At the receiver, in addition to the usual receiving apparatus, a second detection system is provided after the detector immediately preceding the audio amplifier of the receiver, together with suitable means for adjusting the amplitude and. phase of the energy obtained from this second detector. system consists only of the disturbing energy which is used to cancel the similar disturbing energy in the output of the first detecting system which also contains the desired program energy. Thus, only the desired program energy The output of this second detection H is introduced into the audio amplifier and loudspeaker of the receiver.

One of the principal objects of this invention consists in providing a program distribution system in which the energy radiated may only be received satisfactorily, in comfort and with pleasure, by the listener by means of an authorized special receiver.

Another object of the invention is to provide a program distribution system in which the program may be received pleasurably in comfort by an authorized listener without interruption and annoyance from advertising talks and matter.

A still further object of the invention consists in providing a system in which the authorized listener pays directly for the service, thus enabling the broadcasting company to furnish selfsustaining programs of high quality free from disturbing advertising matter.

All of the above desirable objects and features and others which will hereinafter be apparent are accomplished by means of the novel arrangement of apparatus and circuits shown in the drawings accompanying and forming a part of this specification and described fully hereinafter.

In the drawings:

Fig. 1 illustrates in block diagram the necessary modifications of the transmitter to accomplish the desired results; and

Fig. 2 illustrates in block diagram the modifications of the receiver required for cooperation with the transmitter shown in Fig. 1.

It will be hereinafter obvious that this novel program distribution system may be utilized with either amplitude or frequency modulation, but for purposes of explanation the specific example of the proposed selective distribution program system is shown and described in conjunction with a frequency modulation system, as such system is particularly adapted to the transmission and reception of high quality programs of wide range, hence of high fidelity. Block diagrams are used in the drawings for the purpose of simplifying the explanation as all of the units of apparatus used to achieve the novel system are standard and well known to those skilled in the art and therefore need no detailed description.

Referring now particularly to Fig. l, which illustrates the modification of a standard FM transmitter in order to achieve this invention, the program source I, which may comprise speech or music in an audio range of from 50 to 15,000 cycles, is connected to the standard transmitter 5 as shown. The source of disturbing energy 2 may provide a steady or interrupted audio frequency tone or an audio tone varying in frequency and, for example, is shown as a 3,000 cycle oscillator, the output of which is connected as shown to the standard transmitter 5. The output of the 3,000 cycle oscillator 2 is likewise used to amplitude modulate, for example, a

a 20 kilocycle oscillator 4 through the medium of the modulator 3. The output of the modulator 3 is likewise connected to the standard transmitter 5. There is thus fed into the standard transmitter for the purpose of modulating the high frequency carrier, the program energy varying from 50 to 15,000 cycles, the disturbing audio energy of 3,000 cycles, and the 20 kilocycle carrier modulated by the 3,000 cycle disturbing audio energy producing side bands of 17,000 kilocycles and 23,000 kilocycles.

It will thus be seen that the disturbing audio tone of 3,000 cycles and the 20 kilocycle carrier modulated with the same disturbing audio tone of 3,000 cycles are mixed with the program energy before introduction into the modulating systern of the standard transmitter 5. There is therefore radiated from the transmitter antenna and ground system 6 and 1 the high frequency carrier modulated with the 3,000 cycles disturbing tone and the 20 kilocycle carrier likewise modulated with the 3,000 audio disturbing tone as well as the program energy. The modulated, or as it may be termed multi-modulated, high frequency carrier is radiated in the usual unrestricted manner and obviously may be received by any receiving set capable of receiving a frequency modulated carrier. However, the 3,000 cycle tone, whether it be continuous, interrupted, or varying in frequency, precludes the possibility of receiving the program in a satisfactory manner in comfort and with pleasure by the listener. He is therefore deterred from listening to the program. The authorized listener provided with a special receiver, as hereinafter described, is able to receive the program with the disturbing tone eliminated and can therefore listen to the program with satisfaction, without annoyance, in comfort and with pleasure.

Referring now particularly to Fig. 2, which illustrates in block diagram the receiver utilized in connection with the invention, and which comprises astandard frequency modulated receiver I0, which may be provided with an antenna and ground 8 and 9, is modified by eliminating the conductors II and [2 shown in dotted lines normally connecting the output of the detector system, immediately preceding the audio amplifier system, to the audio amplifier system of the receiver and connecting the output of the detector system and the input to the audio amplifier and loudspeaker to the input and output,

respectively, of a kilocycle low pass filter [3.

This filter permits the passage from the output of the detector system of the receiver to the input ofthe audio amplifying system of the program frequencies of 50 to 15,000 kilocycles and the 3,000 cycle disturbing audio tone.

However, a selector l4 comprising a 1'7 to 23 kilocycle band pass filter is connected to the output of the detector system of the receiver as shown, and its output is connected to a second detector system l6. The selector l4 passes the kilocycle carrier modulated with the 3,000 disturbing tone and the two side bands formed by such modulation into the second detector I6 which serves to demodulate the 20 kilocycle car rier and to pass from its output only the 3,000 cycle disturbing tone. The output of the second detector [6 is connected to an amplitude and phase adjustment system l5 whereby the amplitude .and phase adjustment of the 3,000 cycle tone is adjusted in amplitude and placed through the connections shown in phase opposition with the 3,000 cycle tone passing into the input of the audio amplifier and loudspeaker from the output of the 15 kilocycle low pass filter l3. The disturbing audio 3,000 cycle frequency is thus com-- pletely eliminated before introduction into the input of the audio amplifier system of the receiver l0 and the program may thus be received satisfactorily by the listener.

While the second carrier is described as a 20 kilocycle carrier or, that is, having a frequency just above audibility, it obviously may be of any suitable frequency provided of course that it is of a frequency lower than the high frequency program carrier. In practice, the energy of the modulated 20 kilocycle carrier is used to modulate the high frequency carrier of the transmitter 5 approximately 10 to 20%, and the 3,000 cycle tone which is fed directly into the transmitter with the program energy modulates the transmitter 5 about 1 to 2%. Obviously the amplitude and phase adjusting means is made readily replaceable to permit changes in the disturbing frequency from time to time where necessary to prevent unauthorized satisfactory reception of the program.

It will be apparent from the foregoing that this invention provides a selective program distribution system whereby a high quality, wide range program of high fidelity may be transmitted and received by authorized listeners provided with special receivers without interruptions of advertising matter, that the service may be paid for directly to the broadcaster by the authorized listener and that therefore the broadcaster may be able to furnish such high quality programs without depending upon revenue from advertisers to defray the cost of the broadcasting; in other words, that the system will be selfsustaining and the broadcaster therefore encouraged to furnish programs of high quality free from annoying interruptions.

While the invention has been thus completely disclosed and described in connection with only one embodiment thereof, it is to be clearly understood that variou changes may be made therein Without departing from the scope and spirit of the invention as defined in the claims.

What is claimed is:

1. A selective program distribution system comprising, means for generating a carrier wave modulated by a program signal, means for modulating said carrier wave with a disturbing audio signal, means for generating a second carrier wave lower in frequency than said first mentioned carrier, means for modulating said second carrier with said disturbing signal, means for modulating said first modulated carrier by said second modulated carrier, a receiving system including a detector system for each of said carriers and means including phase and amplitude adjustment means for combining the output of said detector systems in phase opposition whereby said disturbing 'sig'nal is eliminated from said first carrier wave.

2. A selective program distribution system comprising, means for generating a first carrier wave modulated with a program signal, means for modulating said first carrier wave with disturbing energy in the audio range, means for generating a second carrier wave differing in. frequency from said first carrier wave, means for mach-dating said second carrier with said disturbing energy, means for modulating said first modulated carrier by said second modulated carrier, a receiving system including two detector systems and means including phase and amplitude adjustment means whereby the outputs of said two detector systems may be combined in phase opposition to eliminate said disturbing energy.

3. A tive program di ibution system comprising, means for generating a high frequency carrier, means for modulating said carrier with program energy, and a disturbing audio frequency signal, means for generating a second carrier of lower frequency than said high frequency carrier, means for modulating said second carrier with said disturbing audio frequency signal, means for modulating said modulated high frequency carrier with said second modulated carrier to produce a multi-modulated high frequency carrier, a receiver for receiving said multimodulated high frequency carrier and including an audio amplifier and loudspeaker, and means for removing said disturbing audio frequency signal prior to the introduction of said program energy into the audio amplifier and loudspeaker of said receiver.

4. A selective program distribution system comprising, means for generating a high frequency carrier, means for modulating said carrier with program energy, further means for modulating said carrier with disturbing energy in the audio range, means for generating a second carrier of lower frequency than said first carrier, means for modulating said second carrier with said disturbing energy, means for modulating said first carrier by said second modulated carrier, means for receiving said high frequency modulated carrier including means for detecting and eliminating therefrom said second carrier and means for combining the disturbing energy carried by said first carrier with that carried by said second carrier and including phase and amplitude adjusting means whereby the disturbing audio energy carried by said first carrier and that by said second carrier are combined in phase opposition.

5. A program distribution system comprising, means for generating a high frequency carrier, means for modulating said carrier with program energy, further means for modulating said carrier with an audio disturbing signal, means for generating a second carrier of lower frequency than said first carrier, means for modulating said second carrier with said disturbing signal, means for modulating said first carrier by said second modulated carrier, means for receiving said high frequency modulated carrier including means for detecting and eliminating therefrom said second carrier and further means for combining said disturbing signal carried by said first carrier with that carried by said second carrier and including amplitude and phase adjusting means whereby the disturbing audio signal is eliminated from said first carrier.

6. A selective program distribution system comprising, means for generating a high frequency carrier, means for modulating said carrier with program energy and a disturbing audio frequency signal, means for generating a second carrier of lower frequency than said high frequency carrier, means for modulating said second carrier with said disturbing audio frequency signal, means for modulating said modulated high frequency carrier with said second modulated carrier to produce a multiplexed high frequency carrier, a receiver for receiving said multiplexed high frequency carrier and including an audio amplifier and loudspeaker and means, including a filter for preventing said lower frequency modulated carrier from entering said audio amplifier, for removing said disturbing audio frequency signal prior to the introduction of said program energy into the audio amplifier and loudspeaker of said receiver.

RICHARD C. CURTIS. 

